With the development of new aircraft generations, the aerodynamic properties first are optimized on models, based on measurements in a wind tunnel. In this regard, numerous filaments of a few centimeters long are attached with a filament end to the model, so that by monitoring the filaments in the wind current, the flow state and the flow direction at the location of the filaments may be determined.
There are roughly three states, specifically, “undisturbed” (or laminar), “disturbed” (turbulent), and “detached”. If the flow lies in the area of a filament on the model surface, then the flow is undisturbed. The filament remains extended (laminar barrier layer) and displays the local direction of the surface flow. From the impact point, the free filament end begins to quiver, the flow is disturbed (turbulent barrier layer). Small, beginning disturbances of the surface flow lead to “quivering” movements of the free filament ends. At the detachment point, the flow rises from the surface (detached flow) and surface currents form that are intensely swirling to back-flowing (counter to the primary flow direction). The filament moves so quickly in all of its spatial degrees of freedom in such an area that only the attached fiber head may be perceived visually.
Until now, the filament images typically are evaluated manually. In this regard, video recordings are taken during the wind tunnel measurements and manually evaluated. In the selected recordings and associated concept sketches, the boundary lines between the areas of undisturbed, disturbed, and detached flow are designated by the user.